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Dry-type resin transformers

We deliver dry-type resin transformers with rated power between 160 and 3150 kVA (up to 20 MVA on request) and insulation level between 1.1 kV and 36 kV, as well as bespoke transformers. Windings made of aluminium foil are vacuum impregnated, which allows reaching optimal thermal parameters.

Transformers for photovoltaic farms

We have dedicated transformers for renewable energy sources, including primarily for photovoltaic farms. Our offer includes transformers for special applications and photovoltaic systems with low losses and high efficiency, with a secondary voltage of 400V, 690V or 800V and a primary voltage of 6kV, 15kV, 20kV or 30kV. As standard, our transformers have voltage (THDu) and current (THDi) harmonic distortion factors of 5% and 10% respectively. For the vast majority of applications, the THD values given above are completely sufficient, but at the customer’s request, we also manufacture transformers with an increased level of harmonics in current and voltage. It is also possible to equip transformers with an electrostatic screen mounted between the LV and LV windings. Transformers are manufactured in accordance with EC Regulation 548/2014 – stage II. Compliance with the standards: IEC 60076-11, EN-50588-1.

Prices of dry-type resin transformer are available after sending a request for proposal.
Transformers available on special request:

  • high-power transformers (up to 20 MVA),
  • for powering converter systems (AC/DC) – 6÷24-pulse,
  • for powering induction furnaces,
  • in primary side insulation class of up to 52 kV,
  • in secondary side insulation class of up to 17.5 kV,
  • for underground purposes, with IP65 protection class (mines),
  • for aqueous purposes, with IP54 protection class (ships),
  • for traction systems (6÷24-pulse, in accordance with IEC 146),
  • for wind farms,
  • single-phase transformers,
  • switchable transformers,
  • transformers with on-load tap changers.

Our offer also includes complete container stations for photovoltaic farms.

Transformers for wind farms

Transformers for wind farms are often associated with non-standard supply voltage on the low voltage side. Most wind turbines operate at a rated voltage of 690V. There are also transformers with a voltage of 400V. The primary side of the transformer is matched to the rated voltage of the network. In Poland, these are mainly 15kV and 20kV voltages. Other voltages 6kV, 10kV, 30kV are also possible.
These transformers are designed to raise the voltage. They should be selected in such a way that the continuous load power does not exceed 80% of the rated power of the transformer.

Oil-immersed transformers

Oil-immersed power transformers are the most numerous group due to the popularity of their applications in electrical power distribution, from high voltage distribution systems to low voltage distribution systems. The name “oil-immersed” derives from being cooled by mineral oils (marked O) or synthetic inflammable oils (marked L). Esters are more and more frequently used for cooling due to their environment friendliness, inflammability and high water solubility index. The operating principle of oil-immersed transformers is different in a way that the transformer core together with winding is located in a metal (steel) box filled with oil. The oil functions as a coolant which receives and transfers heat to external walls of the box. The shape of the metal box is usually corrugated, owing to which the cooling efficiency is far higher. Natural cooling proves successful in transformers with power of up to 4000 kVa.

Construction of an oil-immersed transformer supporting higher power values, namely up to 20 MVA, requires the application of cooling with forced circulation by means of special pumps. This solution makes use of an additional radiator. Owing to a system of protective devices warning of any changes in oil temperature, oil level and pressure inside, one can react to disturbing phenomena and potential defects in advance. 

We are capable of delivering transformers of up to 20 MVA on special request. The cost of a transformer depends on a specification. We prepare an individual offer in response to each request for proposal. 

Download a catalogue of oil-immersed transformers and get to know their specifications and price list.

Three-phase transformers

EG-CR-T transformer with a power of 6.3 MVA 21/6.3kV

Three-phase transformers are used everywhere there is a need for a cheap, efficient and cost-effective transformation and transmission of electrical power. Most frequently, these are 3-phase oil-immersed transformers (but 3-phase dry-type resin transformers are also offered). The former are cooled with oil, the latter with air. The essence of a transformer is the possibility of connecting transmission systems with different voltage levels while preserving the initial frequency. A 3-phase power transformer has made electrical power more widespread, owing to considerably lower power losses. The construction of a three-phase transformer can be executed in two ways: either by an appropriate connection and configuration of single-phase transformers or by applying a three-column arrangement.

We distinguish several types of connections: zigzag, star, with outer or secret zero point. The selection of optimal connection depends on the power supply system, transformer power, level of voltages and economic reasons. The ultimately selected type of connection will result directly from a more in-depth analysis of the entire power supply system. These devices are responsible for efficient reduction of voltages from transmission lines to distribution lines. That is, to voltages from the range between 230 V and 400 V.

We encourage you to become familiar with three-phase transformers offered by EG System. Technical specifications and price lists are available after sending a request for proposal.

Single-phase transformers

EG-CR-T transformer with a power of 3110 kVA 11-6.35/0.36 kV
(double primary voltage)

Single-phase transformers represent the basic element of the electrical power system. The structure of a single-phase transformer consists of a core and at least two windings: primary, which collects electrical power from, for example, the system, and secondary, which returns electrical power with previously altered parameters. The principle of single-phase transformer operation

boils down to supporting one phase. It is similar to the operation of a three-phase transformer, only that we have a single power supply cable in a single-phase transformer. Single-phase power transformers are not that widespread in industry or power generation as the three-phase equivalents. They are used to support lower power values. The application of single-phase transformers is widespread in telecommunications, telecommunications engineering, automation or communication. That is, everywhere one needs lower voltages.

At EG System we make every effort to meet our clients’ demands. Our offer includes such devices. They distinguish themselves through their reliability, efficiency, easy assembly and operation. The transformers we offer meet the following restrictive standards: EN/IEC 61558; EN/IEC 6072IEC 60076-1; 60076-2; 60076-5; 60076-10; 60076-11. They are made of high quality, certified materials, therefore they are capable of meeting the requirements of durability and reliability standards. Our transformers are operated both in Poland and abroad. We also offer solutions allowing the manufacturing of transformers with dual primary voltage.

Housed transformers

EG-CR-T transformer with power of 400 kVA 10/0.42kV in an IP31 housing

There is very often the need to protect the transformer against external factors as well as to fence it and prevent people from touching it.

Our standard variants offer housings with IP21/23/31 protection class. We can also equip a special transformer with an IP54 and IP66 protection class housing.

Switchable transformers

EG-CR-T switchable transformer with a power of 2000 kVA 10-20/0.415kV

When the change of the supply voltage is foreseen, the application of a switchable transformer is a popular solution. This type of a transformer offers a possibility of switching the voltage from one level to the other by means of a jumper.

Thanks to this type of structure there is no need to purchase a new transformer supporting a different voltage value.

Transformers cooperating with inverters

EG-CR-T transformer with a power of 1250 kVA 6.6/0.715 kV for interaction with 6-pulse inverters

There is often the need to apply a special structure of a transformer due to its operation in conditions of increased level of harmonics or floating loads.

We offer transformers for interaction with 6- and 12-pulse inverters with additional insulation, thus allowing the application of such unit to supply power to inverter and converter systems.

Increased voltage transformers

EG-CR-T transformer with a power of 1600 kVA 45/0.42 kV

We manufacture standard transformers with an insulation level of 17.5 kV, 24 kV of 36 kV. We are capable of delivering transformers with insulation level of up to 52 MVA on special request.


The photo presents a transformer with a 45/0.42 kV gear.

Transformers with on-load tap changers

A transformer equipped with an on-load tap changer

Standard transformers are manufactured with voltage-free tap changer with tapping adjusted to client requirements.


Although such solution is usually sufficient for distribution transformers, there is often the need at higher power values to apply an on-load tap changer.

Power transformers

Manufactured in accordance with IEC 60076 standard (or different – upon client request). A core is made with low loss of steel sheet, of crystal with high degree of permeability, with a 45° angle cone in the stepper part. It contains cooling channels.
Windings are made of E-CU 99.9% of electrolytic copper. Windings can be continuous or interrupted by discs, straight or multi-twisted.

Cooling channels are made of appropriately shaped rods and guide rings. Voltage tapping takes place on the GN side by means of a load-free or on-load tap changer.
Windings are dried in an autoclave to achieve accurate measurements and successively avoid non-elasticity. A complete transformer is enclosed in a container and filled with oil in a vacuum.

Transformers can be equipped with additional accessories, such as a pressure relief valve, a preserver with a membrane, current transformers, winding temperature indicator, cable box, a switching station – distribution box, etc.
Transformer installation can be performed on site by our employees.

A voltage-free tap changer is used for stepped (for example, by 2.5%) change of a gear on the GN side of the transformer. If necessary, the tap changer handle, which is usually located on a lid – can be located on the side of a container with manual or engine drive.

On-load tap changer (OLTC) changes the transformer gear when active, thus providing uninterrupted operation. It is activated through an engine. Drive shafts and mechanical bevel gears connect the engine to the on-load tap changer. An electronic voltage regulator detects voltage changes and automatically powers the engine.
OLTC is built according to the state-of-the-art technologies.

Apart from distribution transformers, EG System delivers power transformers for various purposes (such as, for example, power supply of auxiliary transformers and connection of sources to the system) and for special purposes (industrial transformers, starting transformers, transformers for analyses, etc.). In most cases power transformers transform high voltage into medium voltage (HV / MV) or medium voltage into medium voltage (MV / MV).

Owing to progress in electrical power engineering, special transformers (6-12-24 V) are often used to supply power to different machines, including pumps, ventilators or engines designed in accordance with IEC 61378-1, taking account of the type of operation, type of transformer and harmonics content.

All electrical and mechanical parameters, including the impact of load, ambient conditions and operation are selected according to client requirements. We analyse each design to come up with changes aimed at perfecting the transformer in technical and economic terms.

EG System boasts high degree of experience on the market. An impressive number of transformers we have delivered have continued to operate for years with satisfying results. Reliability of transformers is guaranteed by a certified quality system ISO9001. Their expected lifetime with preserved normal performance amounts to 30 years.

Oil-immersed transformers are manufactured with parameters in the following ranges:

Power: from 5 MVA to 45 MVA ONAN (to 63 MVA ONAF)
Lower voltage: 11/15/20/30/52/70 kV
Upper voltage: 90, 110, 123, 132, 150 KV
Frequency: 50-60 Hz
Standards: PN-IEC 60076-13/ IEEE C57.12.01

Each transformer is subject to separate quality tests. The following activities are performed:


• Gear measurement and vector voltage test

• Electrical strength test

• Applied voltage test

• Measurement of winding resistance

• Measurement of lack of idle losses and currents

• Measurement of short-circuit voltage and load losses

• Partial discharge measurements

• Temperature increase test

• Lightning impulse voltage tests

• Noise level measurement

• Short-circuit strength test

All routine tests are performed in a laboratory and are included in the delivery price. Extra tests performed on client request are chargeable. They can be performed at the presence of the client or his/her representative.

Other solutions

EG-CR-T transformer with a power of 2500 kVA 20/0.425 kV, with secondary insulation increased to 3.6/10/20 k

Our offer includes numerous non-standard solutions that help us adjust to the requirements of our clients.

Apart from the abovementioned solutions, it is possible to manufacture a special transformer with low voltage outlets from the bottom, increased insulation of the secondary side and additional accessories.

About the transformers

The name transformer stems from Latin (to transform). Therefore, their main function is to change the parameters of the transmitted energy of the alternate current from voltage X to voltage Y. The phenomena of electromagnetic induction and magnetic field are used. Transformers are applied everywhere there is a need to adjust the power supply parameters to the parameters of the receiver. It was owing to transformers that a possibility of relatively cheap transmission of electrical energy along great distances appeared.

Transformers are used in electrical devices and networks to change the voltage in alternate current circuits. The need for such a change results directly from the need to maximise the efficiency of transmitting electrical power along large (energy transformers – usually applied in high and medium voltage systems) and small distances (low power transformers). 

A broad scope of specialist applications forces manufacturers of transformers to be able to create devices tailored to individual needs and according to predefined specifications. This group includes furnace, welding, safety or rectifier transformers.

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